Effect of space layer doping on photoelectric conversion efficiency of InAs/GaAs quantum dot solar cells

摘要

We report an effect of photoelectric conversion efficiency (PCE) by space layer doping in InAs/ GaAs quantum dot solar cells (QDSC) and δ-doped QDSC grown by molecular beam epitaxy. The PCEs of QDSC and δ-doped QDSC without anti-reflection coating were 10.8% and 4.3%, respectively. The QDSC had about four electrons per QD, and its ideality factor was temperature-independent, which implies that recombination of electron-hole pairs is suppressed by strong potential barriers around charged dots. From the deep level transient spectroscopy measurements, four defect levels, including QD with the activation energy ranges from 0.08 eV to 0.50 eV below GaAs conduction band edge, appeared. Especially, the Ml defect (E_c-0.14 eV) was newly formed in δ-doped QDSC and its density was higher than those of M3 (E_c-0.35 eV) and M4 (E_c-0.50 eV) levels in QDSC. These results suggest that the photo-carriers recombining at Ml defect might be responsible for the reduction of PCE in δ-doped QDSC.